It is well known that a thermistor is used as a temperature detecting element of a temperature sensor used for various purposes.
A temperature sensor adapted to detect temperatures of hot water from a water heater, various atmospheres, and the like adopts a configuration in which a thermistor is housed in a closed-end cylindrical casing and only the casing is exposed in a fluid flow path (see, for example, Patent Literatures 1 to 5). This is intended for insulation between the sensor and fluid, waterproofing, and the like.
Also, some temperature sensors are equipped each with two thermistors (see, for example, Patent Literature 6). Thus, if one of the thermistors fails, temperatures can be detected using the other thermistor. Also, it is possible to troubleshoot the thermistors by comparing detected temperatures between the two thermistors.